Numerous types of vehicles are frequently used on terrain where it is difficult for pneumatic tires to operate. Both military vehicles, such as tanks and amphibious vehicles, and civilian vehicles, such as tractors and recreational vehicles, are sometimes utilized on terrains which are very soft, for example sand surfaces. Pneumatic tires are not capable of efficient operations on such soft surfaces, as they tend to burrow into the surface, rather than riding across it.
In the past, the most popular types of traction bands for use on heavy vehicles have been those using metallic links.
Recently, elastomeric endless traction bands have become popular due to an increase in the number of construction sites where vehicles having traction bands must also drive on the pavement and because there is also a demand for vehicles used for low soil compaction farming, and over snow covered, very uneven, or muddy terrain. With the combination of elastomeric technology and a tremendous amount of trial and error, various types of traction bands using elastomeric materials are now available in the industry. They are used on excavators, dump carriers, boring machines, combines, tractors, and the like.
While endless traction bands using elastomeric materials are often desirable since they reduce damage to the terrain over which they are used, reduce noise and allow access to various types of soil, they do have some drawbacks concerning their use. Once installed, the traction band is usually carried and maintained in tension by a plurality of rotating elements (e.g. sprocket wheel, tension wheel and road wheels) that are connected to the vehicle. The rotating elements cooperate with the inner surface of the traction band which generally comprises a plurality of guide lugs and drive lugs, respectively ensuring lateral support and power transmission to the traction band. The guide lugs are disposed in one or more rows along the inner circumference of the traction band in order to offer lateral guidance by restraining the relative motion of the wheel-band assembly. The drive lugs are disposed in one or more rows along the inner circumference of the traction band in order to provide power transmission by meshing between with the sprocket wheel.
However, since elastomeric traction bands are more easily deformed than metal bands, the wear and the use of the traction band under extreme conditions sometimes lead to de-tracking occurrences. De-tracking is mostly initiated by a combined action of friction and interference between the wheels and the guide lugs, which induces a lateral deformation of the elastomeric guide lugs. At this stage, the wheels are misaligned with the traction band and as the traction band continues to rotate and the guide lugs keep on laterally deforming, the rotating wheels sometimes climb on the lateral sides of the guide lugs, until de-tracking of the traction band is observed.
To avoid this problem, different guide lug configurations have been created from various elastomeric compositions or shapes. For instance, Tsunoda et al. (U.S. Pat. No. 6,300,396B1) and Muramatsu et al. (U.S. Pat. Nos. 5,447,365 and 5,540,489) have inserted plate-like member in the guide lugs whereas Tsunoda et al. (U.S. Pat. No. 5,984,438) have inserted rod-like member. The members have some low-friction surfaces exposed to the outside of the guide lugs which contact and collide with the wheels. These low-friction materials reduce de-tracking occurrences but to be effective, they need a direct contact with a wheel. Also, the lateral movement of the guide lugs with respect to the track is not significantly diminished under high lateral loads, even if a member has been inserted in the guide lug.
In Hori (U.S. Pat. No. 5,380,076), Togashi et al. (U.S. Pat. No. 5,295,741) and Ono (U.S. Pat. No. 6,176,557), core bars for crawler-type tracks are partially inserted in the elastomeric material, having a central portion which is not embedded in the elastomeric material and acts as a guide lug, and laterally extending winged portions which are embedded in the elastomeric material and which generally provide lateral rigidity to the track. Even though core bars are rigidly connected with respect to the track, the “guide lug” portion of the central portion has a shape configuration which is restricted to the configuration of the wheels. Additionally, since the guide lug portions of the core bars are integrally formed with the laterally extending winged portions, lateral forces applied on the guide lug portions will tend to induce a rotational and/or torsional movement of the whole track, thereby increasing the probability of de-tracking. Also, by locating the core bars near the inner surface of the track, the portion of the elastomeric material located between the neutral axis of the track and the inner surface thereof can be subjected of high level of compression. At high speed, these high levels of compression can generate excessive heat in the elastomeric material which may provoke delamination and ultimately failure of the track. Moreover, core bars are usually heavy and tend to induce excessive vibrations when the vehicle is used at high speed.
Since it is almost impossible to laterally or longitudinally enlarge the guide lugs because of their localization into the spacing generated by each wheel assembly, de-tracking events may still occur, especially when such a traction band is installed on a heavy and fast vehicle, like a military vehicle.
The present invention sets out to solve the problem associated with de-tracking events by providing a novel endless track construction.